Solar cells are semiconductor devices that are usually manufactured from silicon-based material. Some solar cells are made from screen printed poly-crystalline silicon. Single crystalline wafers can be used to make very efficient solar cells. However, high manufacturing costs for making single crystalline materials makes the large scale production of solar cells from these materials impractical.
Poly-crystalline silicon wafers used to manufacture solar cells are made by cutting 180 to 350 micrometer thick wafers from block-cast silicon ingots. The wafers are usually lightly p-type doped. To make a solar cell from the wafer, a surface diffusion of n-type dopants is performed on the front side of the wafer. This forms a p-n junction a few hundred nanometers below the surface. Solar cells usually also include anti-reflective coatings, such as silicon nitride or titanium dioxide and/or have textured surfaces increase efficiency of light absorption. This method is disadvantageous in that the crystal takes an exceptionally long time to grow on the silicon ingot.
Metal contacts are formed on the back and front surfaces of poly-crystalline silicon wafers by screen-printing metal pastes, such as silver paste or aluminum paste. After the metal contacts are formed, the solar cells are assembled into panels and are sandwiched between glass and polymer resins.
As mentioned above, solar cells and solar panels that are formed from single crystal silicon are preferred because of the efficiency of the solar cells and panels made from single crystal silicon.